Crown Com-Tech CT-400 Manuel de service télécharger pdf (Page 12)

Com-Tech 400 Amplifier Service Manual

Electrical Checkout Procedures

General Information

The following test procedures are to be used to verify

operation of this amplifier. DO NOT connect a load or

inject a signal unless directed to do so by the proce-

dure. These tests, though meant for verification and

alignment of the amplifier, may also be very helpful in

troubleshooting. For best results, tests should be

performed in order.

All tests assume that AC power is from a regulated 120

VAC source. Test equipment includes an oscillo-

scope, a DMM, a signal generator, loads, and I.M.D.

and T.H.D. noise test equipment.

Standard Initial Conditions

Level controls fully clockwise.

Stereo/Mono switch in Stereo.

Sensitivity switch in 26 dB fixed gain position.

70-V mode switches in the 8/4 ohm position.

It is assumed, in each step, that conditions of the

amplifier are per these initial conditions unless other-

wise specified.

Test 1: DC Offset

Spec: 0 VDC, ±10 mV.

Initial Conditions: Controls per standard, inputs shorted.

Procedure: Measure DC voltage at the output connec-

tors (rear panel). There is no adjustment for output

offset. If spec is not met, there is an electrical malfunc-

tion. Slightly out of spec measurement is usually due

to U104/U204 out of tolorance.

Test 2: Output Bias Adjustment

Spec: 300 to 320 mVDC.

Initial Conditions: Controls per standard, heatsink tem-

perature less than 40°C.

Procedure: Measure DC voltages on the output module

across R31 (15 ohm), adjust R26 if necessary. Mea-

sure DC voltages on the output module across R32 (15

ohm), adjust R23 if necessary. Repeat for second

channel.

Test 3: ODEP Voltage Adjustment

Spec: Bias Per Chart, ±0.1V DC.

Initial Conditions: Controls per standard, heatsink at

room temperature 20 to 30°C (68 to 86°F). Note: This

adjustment should normally be performed within 2

minutes of turn on from ambient (cold) conditions. If

possible measure heatsink temperature, if not mea-

sure ambient room temperature. Use this information

when referencing the following chart.

The following list of ODEP bias voltages VS. tempera-

ture is based on the use of Main Modules built on any

circuit board up to and including the D 7993-5 board.

°F °C V

–ODEP

+ODEP

66 18.9 –10.31 11.41

68 20.0 –10.26 11.36

70 21.1 –10.20 11.30

72 22.2 –10.14 11.24

74 23.3 –10.09 11.19

76 24.4 –10.03 11.13

77 25.0 –10.00 11.10

78 25.6 –9.97 11.07

80 26.7 –9.91 11.01

82 27.8 –9.86 10.96

84 28.9 –9.80 10.90

86 30.0 –9.74 10.84

88 31.1 –9.69 10.79

90 32.2 –9.63 10.73

92 33.3 –9.57 10.67

94 34.4 –9.51 10.61

The following list of ODEP bias voltages VS. tempera-

ture is based on the use of Main Modules built on any

circuit board after the D 7993-5 board.

°F °C V

–ODEP

+ODEP

66 18.9 –10.31 10.31

68 20.0 –10.26 10.26

70 21.1 –10.20 10.20

72 22.2 –10.14 10.14

74 23.3 –10.09 10.09

76 24.4 –10.03 10.03

77 25.0 –10.00 10.00

78 25.6 –9.97 9.97

80 26.7 –9.91 9.91

82 27.8 –9.86 9.86

84 28.9 –9.80 9.80

86 30.0 –9.74 9.74

88 31.1 –9.69 9.69

90 32.2 –9.63 9.63

92 33.3 –9.57 9.57

94 34.4 –9.51 9.51

–ODEP Procedure: Measure pin 3 of J500 and, if neces-

sary, adjust R121 to obtain V

–ODEP

as specified above.

Measure pin 3 of J500 and, if necessary, adjust R221

to obtain V

–ODEP

as specified above.

+ODEP Procedure: Measure pin 4 of J500 and, if neces-

sary, adjust R132 to obtain V

+ODEP

as specified above.

Measure pin 4 of J500 and, if necessary, adjust R232

to obtain V

+ODEP

as specified above.

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Crown Com-Tech CT-400 Manuel de service Page 12

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